1. Field of the Invention
This invention relates to the field of optical communications. More particularly, the invention relates to an optical communication system which uses a plurality of carrier wavelengths on the same optical fiber.
2. Background Information
In optical communication it is desirable to use multiple wavelengths to increase the data bandwidth through an optical channel such as an optical fiber. In such a wavelength multiplexed optical system, where there are several carriers operating within the same optical fiber, there is the possibility that unwanted interferences are formed somewhere in the available optical band. It is well known that the fiber optical medium is non-linear and, while second harmonic distortions produce sums of differences of the traveling wavelengths which tend to lie outside the band of interest, the third harmonic distortion can have an interfering effect within the carrier spectrum, so that severe contamination of a channel by another channel can occur. This is particularly the case for wavelengths synthesized in a wavelength division network and distributed along an optical fiber. Unwanted harmonics within the optical communication channels interfere with the location of present carriers being transmitted as well as interfering with the insertion of a new carrier in the same location of the optical spectrum. It would be desirable to control the location of unwanted harmonics within the optical carrier wavelengths to avoid the existing optical channels and permit the addition of new carriers.